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Talgonadia 07-02-2012 03:44 PM

Adding return air supply
 
I added central air to my ranch style house and it's having trouble keeping at 74 during the day. None of my rooms have a return air vent so I figure this is the cause. The AC is unable to circulate the air. The heat has nowhere to go. I thought of using insulated flex tubes to the furnace.

I would have 6 return air registers in all. 2 in living room, 2 in master bedroom, and 1 in each bedroom. My house is open floor so the kitchen and dining room are connected to the living room so I thought no need for return vent.

I was hoping to run the flex tube from each vent through the attic? It is accessible so easy to run and that way my return vents are up high. I would then have all the flex tubing connect to a return air plenum.

This would be cheaper because I could do all that work at my expense then hire a sheet metal hvac to finish the plenum and connect the flex duct.

My question, would this work. I read that flex pipe shouldn't be used in length greater than 15ft due to pressure from the returns.

beenthere 07-02-2012 05:01 PM

for the rooms far a way from the furnace, you will nee bigger then 6" flex.

Talgonadia 07-02-2012 05:04 PM

Why would they need to be larger?

beenthere 07-02-2012 05:09 PM

longer run, less air flow. Due to resistance of the duct.

scottmcd9999 07-02-2012 07:28 PM

IMO flex shouldn't be used for returns, except for very short connectors (under 8'). Many do use it for returns, of course, but if you do then heed beenthere's advice - flex duct is a LOT more restrictive than metal duct, so you must be sure to adequately size it.

A better question is why you think you need to install returns in every room. While there's really nothing wrong in doing that, if your current return system is adequately sized and properly located, you'll gain very little by doing this.

Are you sure the A/C is properly sized, installed, and charged? I'd be more inclined to investigate that first. For example, what size ducts are running to the individual rooms? Most areas need at least 6" ducts, and some will need 8" or perhaps larger. If this was a heat-only conversion, then many of those systems were far too small to handle the larger volumes needed for air conditioning.

So before you spend a lot of time and energy (and money) on something with little potential, be sure that you're chasing the right tail :)

Talgonadia 07-04-2012 09:13 AM

The problem is I have no return ducts at all. I thought I made that clear. No return ducts no air circulation. I've had 4 contractors come in now to look and are getting me bids. I just found out now that there is no room above to run ductwork so if it was done it would have to be ran in the basement.

My furnace is the mobile home type and only blows down. Due to this all 4 contractors say I'd need to get a new furnace since it is currently upstairs blowing down.

Not sure if they are just trying to get more $$ or are serious due to the ducting.

I am going to repair the hole in the ductwork by cutting a 3 side square and taping the hole on top from the inside. Once that is done I'll push the cut ductwork back and tape it. That should be good enough?

Talgonadia 07-04-2012 09:19 AM

They have all said my duct is properly sized and the ac unit should be fine. Due to the loss in airflow from the hole and poor circulation I thought was the cause. Once I patch that hole I'll check.
It was 100 degrees here in WI and the house stayed at 79. I have it set at 74... If the unit is not properly sized I'd be very mad... I had 4 good reviewed bids on the central air...

scottmcd9999 07-05-2012 06:07 AM

I'm not sure what you're referring to with "repairing the hole". Perhaps you could post some pictures that show what you're referring to?

Was the system installed by a contractor? You mention 4 bids, so I assume it was. If so, why was there no return system installed?

Talgonadia 07-05-2012 07:18 AM

When I get done with work I'll post pictures. I fixed the leaky duct with tape so now my supply registers are better.

I'm not sure why this house doesn't have return air. It's a double wide manufactured house. I'll ask my neighbors if theirs has any... I have another question. On my furnace where the filter is I have a plenum that sucks air in from the laundry room and from outside. Is the line that sucks air from the outside needed? I'm asking this because the air being sucked in is 95-102 and it would only take more energy to cool it. The top of the plenum is open so it should be sucking more than enough air?...

Talgonadia 07-05-2012 09:46 AM

I didn't mention this. We bought a foreclosed house and when we bought it the outside compressor unit was missing so I got a new ac unit and coil installed

Talgonadia 07-06-2012 11:02 AM

I'm thinking of running the ductwork myself... I would go from my furnace through a wall to my kitchen area. I would then run the ductwork along the wall and ceiling. I could then go through the wall to my bedroom and have access to my bedroom and living room.

The furnace filter is 20x20 but my plenum is 18x20. If I went with 8x14 ductwork would that starve the furnace of return air? What would you guys recommend I do? I could always leave part of my plenum u
Open to suck air from the laundry area...

scottmcd9999 07-07-2012 08:05 AM

So this is a manufactured home? If so, then most of those furnaces are not designed to use ducted returns, and you'd have to be VERY careful to insure that you have sufficient air flow back to the system. Most stick-built homes today don't have returns in every room - they would have one or two centrally located returns (like yours). Granted it's better to have returns placed in each room, but from what you've described as your plan of action, I can't see it making any difference, and in fact it could cause more troubles (restricted returns, etc etc).

That said - in my experience, if you're having troubles cooling a doublewide manufactured home, the first thing you need to do is insure that you have crossovers placed in the right locations. Crossovers are the ducts that connect the two sections of the doublewide, and you would be best served by having one on each end of the home. In my experience that gives you the best airflow, and can eliminate a lot of the dead air areas. We've also taken to using hard pipe for the crossovers. Flex crossovers tend to degrade and collapse, and they are far more restrictive than are hard pipe crossovers.

I'd do that long before I'd start running return ductwork.

Quote:

Is the line that sucks air from the outside needed?
The only purpose of that is to introduce fresh air into the structure (many states/cities require that outside air be brought in). You could remove it, but it could violate codes in your area. I seriously doubt it affects your overall performance.

Talgonadia 07-07-2012 02:35 PM

2 Attachment(s)
Here are two pictures I have. One is a picture of the furnace and you can see how it has a plenum on top that has the duct that sucks in air from the outside. The top of the Plenum is not covered so the furnace only pulls air in from the laundry room. What do you guys think I should do to help my AC cool. I have checked my ductwork and it appears to be fine now. I fixed the holes and my air flow to the rooms seem adequate. I'm in the process of having an energy audit. I was really hoping that adding the ductwork the return air would suck from the middle of the house which to me makes sense.

I'm no expert so I dont want to add ductwork and just have it make my furnace be less efficient due to the ductwork restricting airflow...

One other thing, i went to my neighbors house who also has a doublewide manufacture house (all the houses around here are) and above all his doors he has vents. His furnace is also located in the middle of his house so his setup seems to be more efficient. His house does not have a basement like mine though :)

Also on the picture I created in paint, the walls for the left side are suppose to be centered. So that makes me bedroom look a little larger and the kitchen smaller :P


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